The present invention relates to a gas turbine combustor and a gas turbine generating apparatus, and more particularly, to a low NOx gas turbine combustor and a low NOx gas turbine generating apparatus which are suitable to use gaseous fuel or liquid fuel.
One of the features of the gas turbine combustor is a very wide operation range from starting to full load. For the application of this wide operation range, it has conventionally been customary to operate the gas turbine combustor by regulating the amount of fuel supplied to burners with the amount of air kept constant as disclosed in Japanese Patent Unexamined Publication No. 61-52523. However, according to the operating method in which only the amount of fuel is regulated, when the load is low, the amount of fuel is reduced during the operation so that the combustion becomes lean on fuel to make it impossible to maintain a good combustion state, resulting in that unburned fuel is increased. To cope with this, it is proposed in Japanese Patent Unexamined Publication No. 61-52523 that, in order to maintain a good combustion state over the whole operation range of a gas turbine and reduce the emission of nitrogen oxides (NOx), a combustion chamber is divided into a primary stage combustion section in charge of the low load operation and a secondary combustion section in charge of the high load operation so as to effect the two-stage combustion and the amount of combustion air for the primary stage and the amount of combustion air for the secondary stage are made changeable independently. The primary stage combustion section adopts a diffusion combustion mode in which fuel and air supplied from different exhaust ports are mixed in the combustion section and combusted, while the secondary stage combustion section adopts a premixed combustion mode in which fuel and air are mixed prior to combustion.
In order to reduce the amount of NOx produced from the gas turbine combustor, it is effective to decrease the temperature of combustion gas. The temperature of combustion gas becomes lower as the amount of air becomes larger when the amount of fuel is kept constant. Namely, as the combustion becomes lean on fuel, the temperature of combustion gas becomes lower to make it possible to reduce NOx. However, in the case of a burner of the diffusion combustion type, even if the amount of air is increased to effect the combustion under the condition of lean on fuel, a region where an excess air ratio becomes close to 1 (one) inevitably appears in the process of mixing fuel and air in the combustion chamber. For this reason, it is difficult in general to reduce NOx and the merit of controlling the amount of air is not so great for the reduction of NOx. On the other hand, in the premixed combustion burner, the NOx emission can be reduced by performing the fuel lean combustion. However, for the fuel lean combustion, it is necessary to keep the fuel-air ratio within a specified range that results in the low NOx emission even if the load of the turbine is changed.
In the above-described prior art, no suggestion is made about the means for keeping the fuel-air ratio within a specified range that results in the low NOx emission even if the load of the turbine is changed.